Combined sewer systems are drain systems in which storm water and sanitary sewage are delivered to wastewater treatment plants in the same tunnel infrastructure. When rainwater or melted snow/ice enters these systems, the amount of sewage and storm water entering a treatment plant may exceed its capacity, resulting in a combined sewer overflow (CSO) that delivers excess untreated sewage and storm water to a local surface water body, such as a river or lake. Over seven hundred communities across the United States have combined sewer systems, and are affected by these overflows, which can be major sources of water pollution. Yearly national expenditures to combat CSOs are estimated to total several hundred million dollars.
One method of reducing CSOs is to perform flow monitoring and real-time control of inline storage. In this method, sensors detect increased water flow, and control valves hold sewage and storm water in place while the wastewater treatment plant processes sewage without exceeding capacity. A new technique to implement this type of control is to use a wireless sensor network. Wireless sensor nodes embedded in manhole tunnels can detect water flow and broadcast sensor data to a base station that can reply with instructions to close flow valves in the sewer system, which are also controlled by the sensor nodes. The wireless sensor network may have multiple hops from an embedded sensor node to the base station.
The task of establishing a radio frequency (RF) network connection between below-ground nodes and above-ground nodes is often difficult because manholes are often located in roadways where vehicles and snow plows run over and scrape the manhole entrances. Therefore radio antennas used to make the connection may be destroyed if they have profiles that extend above road grade level.